"Primary Constructor Parameters are Mutable Fields"

public sealed class User(string name, int age) {
	public void PrintNameAndAge() {
		Console.WriteLine($"User name: {name}, Age: {age}");
	}

	public void PrintNameAllCapsIfOld(int oldThreshold) {
		if (age >= oldThreshold) {
			name = name.ToUpperInvariant(); // Oops- did we really mean to change this permanently for this User instance?
		}

		Console.WriteLine(name);
	}
}

static void Test() {
	var user = new User("Ben", 33);
	user.PrintNameAllCapsIfOld(30); // "BEN"
	user.PrintNameAndAge(); // "User name: BEN, Age: 33" -- we've accidentally altered the name field in the previous method invocation
}